The Copper Mountain Coal occurrence outcrops along the old Copper Mountain railway, 1.5 kilometres south-southwest of Princeton.

The coal prospect is in the south-central part of the Princeton Basin, a northerly trending fault-bounded trough filled by Eocene volcanic rocks of mainly intermediate composition, comprising the Lower Volcanic Formation, and an overlying Eocene sedimentary sequence of sandstone, shale, waterlain rhyolite tephra (tuff) and coal, up to 2000 metres thick, comprising the Allenby Formation.

The deposit is up to 35 metres stratigraphically below the Golden Glow coal zone, one of four significant coal-bearing zones in a 530-metre section in the Allenby Formation (Princeton Group) (Paper 83-3, Figure 13B).

The railway cut exposes a seam of clean coal, up to 2.13 metres thick, overlain by 0.48 metre of bentonite and underlain by 1.5 metres of conglomerate (Paper 83-3, Figure 13B, section 15).

A second coal seam in sandstone occurs along the railway, 350 metres to the north. The seam is up to 1.80 metres thick, including a thin band of shale, and contains up to 152 centimetres of clean coal (Paper 83-3, Figure 13B, section 16).